Variable light intensity lamp socket having semiconductor mounted on heat sink thermally isolated from lamp base

ABSTRACT

A solid state controllable current conducting semiconductor of a variable light intensity control circuit is mounted on a heat sink member which is positioned adjacent one end of an electrically and thermally insulating support member. The opposite end of the support member is secured to the insulating disc at the base of the lamp receiving shell of the lamp socket. The heat sink member is shaped to provide structural support and to increase the surface area thereof.

United States Patent Melvyn B. Grindstaff DiaI-A-Lite Co., ProfessionalBldg., Bartlesville, Okla. 74003 Feb. 10, 1969 Apr. 6, 1971Continuation-impart of application Ser. No. 558,784, June 20, 1966, nowabandoned.

Inventor Appl. No. Filed Patented VARIABLE LIGHT INTENSITY LAMP SOCKETHAVING SEMICONDUCTOR MOUNTED ON HEAT SINK THERMALLY ISOLATED FROM LAMPBASE 8 Claims, 6 Drawing Figs.

US. Cl. 315/194, 315/195, 315/197, 315/200, 315/241, 25/50 Int. Cl..H05b 37/02, G05f I/OO Field of Search 315/194- --200, 241, 50;307/297; 317/21, 101

References Cited UNITED STATES PATENTS 3,256,466 6/1966 Trolio et al. 3l5/200X 3,275,922 9/1966 Meyer et al.... 3l5/200X l/l967 Duncan 315/194X3,331,013 7/1967 Cunningham 315/194X 3,346,874 10/1967 Howell 307/2973,401,265 9/1968 3l7/l0lX 3,450,941 6/1969 Butts 315/194 OTHERREFERENCES Triac Control For A-C Power, By E. K. Howell, GeneralElectric Application note, May, 1964 pages 1 to 6 (and title P Using theTriac for control of AC power, General Electric Application note, March,1966, pages 1 11 only (and title P Primary Examiner-John W. I-IuckertAssistant Examiner-Andrew J. James Attorney-J. E. Phillips ABSTRACT: Asolid state controllable current conducting semiconductor of a variablelight intensity control circuit is mounted on a heat sink member whichis positioned adjacent one end of an electrically and thermallyinsulating support member. The opposite end of the support member issecured to the insulating disc at the base of the lamp receiving shellof the lamp socket. The heat sink member is shaped to provide structuralsupport and to increase the surface area thereof.

Patented April 6, 1971 r 3,573,543

32 K9 2 0. TB

FIG. 3

INVENTOR. MELVYN B. GRINDSTAFF VARIABLE LIGHT INTENSITY LAMP SOCKETHAVING SEMICONDUCTOR MOUNTED ON HEAT SINK THERMALLY ISOLATED FROM LAMPBASE This application is a continuation-in-part of my copendingapplication, Ser. No. 558,784, filed Jun. 20, 1966, now abandoned.

This invention relates to variable light intensity lamp sockets. In oneaspect the invention relates to an improved construction of a lightdimming socket for avoiding overheating of the components thereof. Inanother aspect the invention relates to a heat sink for utilization in avariable light intensity control circuit mounted in a standardincandescent lamp socket.

This invention represents an improvement over the prior art lamp dimmersexemplified by Duncan, US. Pat. No. 3,300,711. In the structureillustrated in the Duncan patent, the anode stud of the semiconductor inthe control circuit is positioned directly against the center contactarm, which in turn is in direct contact with the center contact of thelight bulb. Furthermore, the anode stud and a portion of the heat sinkchassis are exposed to radiation from the lamp receiving shell. Thistype of structure permits heat transfer between the lamp and thesemiconductor.

In accordance with the present invention, it has been discovered thatthe thermal isolation of the semiconductor of a variable light intensitycontrol circuit positioned in a lamp socket from the lamp receivingshell can be significantly enhanced by securing the semiconductor on aheat sink positioned on the remote end of an electrically and thermallyinsulating support member which is mounted substantially perpendicularlyto an electrically and thermally insulating base disc positioned on theinner end of the lamp receiving shell.

Accordingly, it is an object of the present invention to pro vide animproved variable light intensity lamp socket. It is an object of theinvention to enhance the thermal isolation of a semiconductor in avariable light intensity control circuit from the heat produced by thelamp. It is an object of the invention to provide an improved heat sinkmounting for a semiconductor. It is an object of the invention toprovide an improved thermal mounting for a semiconductor at a lowercost. It is an object of the invention to provide a wide range of lightintensity control within a standard lamp bulb socket without dimensionalmodification thereof.

Other objects, aspects and advantages of the invention will be apparentfrom a study of the specification, the drawings and the appended claimsto the invention.

In the drawings, FIG. 1 is a schematic representation of a circuitsuitable for utilization with the invention; FIG. 2 is an exploded view,partly in perspective and partly in elevation of a variable lightintensity lampholder in accordance with a presently preferred embodimentof the invention, showing the back side of the structural support board;FIG. 3 is a partial view in elevation of the front side of thestructural board, showing the structural and spatial relationship of thecomponents; FIG. 4 is a cross-sectional view along line 4-4 in FIG. 3;FIG. 5 is a view along line 5-5 in FIG. 4; and FIG. 6 is a perspectiveview of the back side of the heat sink element.

Referring now to FIG. 1, one lead of light 11 is connected to a firstterminal 12 of an AC power source 13, while the other lead of light 11is connected to a first terminal 14 of the variable light intensitycontrol circuit 15. A switch 16 is connected between the second terminal17 of power source 13 and a second terminal 18 of circuit 15. A firstmain current carrying terminal 19 of a solid state controlledbidirectional current conducting semiconductor, or triac, 21 isconnected to terminal 14 while the second main current carrying terminal22 of semiconductor 21 is connected through inductance 23 to terminal18. A capacitor 24 is connected between terminals 14 and 18. Capacitor24 and inductance 23 serve as a radio frequency filter to prevent thepulsing in circuit from affecting AM. radio reception. The constructionand operation of the triac 21 are described by J. H. Galloway in "Usingthe Triac for Control of AC Power," General Electric Application Note,Mar. 1966. A variable resistor 25 and a capacitor 26 are connected inseries between tenninals 14 and 22. A resistor 27 and a bidirectionaldiode 28 are connected in series between the gate terminal 29 of triac21 and the junction between resistor 25 and capacitor 26. A capacitor 31is connected between terminal 22 and the junction of resistor 27 andbidirectional diode 28. A resistor 32 is connected in parallel withvariable resistor 25 to provide the desired light level at the low endof the light intensity control range. Resistor 25 is manually varied toadjust the desired light level within the control range. Resistor 25 andswitch 16 can be combined in a single unit actuated by knob 33 (FIGS. 3and 5). In the operation of the circuit, the rotative positioning ofknob 33 controls the amount of current through diode 28 to the gateterminal 29 of triac 21 and hence gives complete intensity control overthe current supply through standard lamp bulb 11.

Referring now to FIGS. 2-6, the light intensity control circuit isinstalled in a conventional lamp socket of standard design comprising anouter housing 36, an electrically and thermally insulating liner 37, cap38, and a threaded screw shell 39 adapted to receive a standard lampbulb. An electrical conduit having leads 43 and 43 connects screwterminals 12 and 17 to the source of power. Screw terminal 12 ispositioned in vertical metal plate 41 which is connected by rivets 42through vertical support board 40 to the vertical portion of L- shapedmetal bar 43. The horizontal portion of bar 43 is connected by rivets 44through electrically and thermally insulating base disc 47 to the innerend of screw shell 39. Thus, bar 43 serves not only as an electricalconnection, but also as the structural mounting bracket for positioningvertical support board 40 substantially perpendicularly to base disc 47on the side thereof remote from shell 39. The spring contact arm 45 ispositioned within screw shell 39 but insulated therefrom, and isconnected by lead 46 to terminal 14.

Vertical support board 40 is formed of a suitable electrically andthermally insulating material, for example, fiberglass. Substantiallyall of the remaining electrical connections are in the form of a printedcircuit 51 on the back side of vertical support board 40. An insulatingpaper sheet 52 is positioned over the printed circuit 51 and secured toboard 40 by a layer of a suitable adhesive and by rivets 42. The upperend of board 40 can be provided with a notch 48 to receive a tab 49 ofsheet 52. Board 40 also serves as the structural mounting means forresistors 25, 27 and 32, capacitors 24, 26 and 31, switch 16, choke 23,and heat sink member 53. Heat sink member 53 is formed of a suitableconductor of heat and electricity, for example, a metal such as copper.As illustrated in FIGS. 3, 5 and 6, heat sink member 53 comprises asubstantially semicircular planar section 54 which is roughly in theshape of a D, mounting lugs 55 and 56 which project rearwardly fromsection 54 into openings in vertical support board 40, inverted U-shapedridges 57 and 58 projecting upwardly from section 54, peripheral flangesections 59 and 61 depending downwardly from section 54, and invertedcup-shaped section or depression 62 extending upwardly from section 54.Planar section 54 extends substantially the distance between supportboard 40 and the adjacent portion of the liner 37. Ridges 57 and 58 aresubstantially perpendicular to support board 40. Ridges 57 and 58 andflange sections 59 and 61 extend rearwardly into contact with verticalsupport board 40, thereby rigidly supporting heat sink member 53substantially perpendicularly to support board 40, preventing bendingrelative to support board 40. Triac 21 and diode 28 are mounted insideof cupshaped section 62 conductive heat transfer relationship therewith,one main current carrying terminal being soldered directly to theunderside of the planar center section 63 of cup-shaped section 62.Thus, element 53 serves as a structural mounting for triac 21, as a heatsink for triac 21 and as an electrical connection to one terminal oftriac 21. Flange sections 59 and 61 and ridges 57 and 58 not only serveas structural mounting elements, their configuration increases the totalsurface area of the heat sink 53, thereby enhancing the ability of theheat sink 53 to dissipate heat produced by internal heating in triac 21.The center section 63 of cup-shaped section 62 is planar to prevent fluxbuildup during soldering as this could cause incomplete surface contactof the terminal of triac 21 with section 63. The cup-shaped section 62encloses the triac 21 to a greater extent than would be possible with aflat surface and thus provides maximum surface area for the heat sink 53in the immediate area of triac 21. While flange sections 59 and 61 canform a single continuous flange around the curved periphery of planarsection 54, it is presently preferred to omit the center section of theflange to prevent the possibility of contact with the potentiometer 25.

As illustrated in FIG. 3, the heat sink 53 is mounted on heat insulativeboard 40 is as remotely as possible from the base disc 47 and the screwshell 39. Bar 43 is the only heat conductive material thermallyconnected to screw shell 39 which is located in the same chamber as heatsink member 53. Unlike many prior art devices which employ a full sizemetal disc, bar 43 is shaped to present a minimum of exposed surfacearea in the common chamber, thereby minimizing transfer of heat fromscrew shell 39 into the chamber. in general the exposed surface area ofbar 43 will be less than 50 percent and preferably less than 25 percentof the area of disc 47. The next most significant heat producer is choke23, which is mounted on thermally insulative board 40 adjacent disc 47and as far as possible from triac 21. As triac 21 requires only a verylow gate current, there is very little heat produced by potentiometer25. While the problem of the heat production by a triac is particularlyacute in the environment of a standard lamp socket structure, the use ofa monodirectional solid state current conducting semiconductor alsopresents significant problems of heat dissipation. The structure of thepresent invention is applicable to both of these types ofsemiconductors.

This invention permits control of a standard lamp bulb from off to anydesired intensity within the limits of the bulb design. The variablelight intensity control circuit, despite the heat sink requirements, hasbeen miniaturized to such an extend that it can be inserted or formedwithin a standard light bulb socket without modification of itsdimensions.

In a presently preferred embodiment of the invention, heat sink member53 is formed from a sheet of copper having a thickness of approximately0.025 inch into the generally D shape illustrated in the drawings,having an initial, or unfolded, diameter of about l inches, planarsection 54 having final dimensions of approximately 1 inch in apparentdiameter and approximately five-eighth inch in the directionperpendicular to support board 40. Cup-shaped section 62 has a depth ofapproximately one-eighth inch deep and smaller and larger diameters ofapproximately three-eighth inch and onefourth inch, respectively. Theheat sink member 53 is mounted on board 40 so that planar section 54 isapproximately one inch from' disc member 47.

Reasonable variations and modifications of this invention can be made,or followed, in view of the foregoing disclosure, without departing fromthe spirit or scope thereof.

lclaim:

l. A variable light intensity lamp socket which comprises a lamp sockethousing having an electrically and thermally insulating interiorsurface, a lamp receiving shell positioned in one end of said lampsocket housing, an electrically and thermally insulating base memberpositioned in said housing and across the inner end of said shell, anelectrically and thermally insulating support member positioned withinsaid housing and sub stantially perpendicularly to said base member onthe side thereof remote from said lamp receiving shell, an electricallyconductive metal heat sink member mounted substantially perpendicularlyto said support member on a portion of said support member remote fromsaid base member so as to be thermally insulated from said shell, saidmetal member being in the form of a generally semicircular planar memberextending substantially the distance from said support member to theadjacent portion of said housing, said planar member having a cup-shapeddepression formed therein, center contact means positioned within andinsulated from said lamp receiving shell, and variable light intensitycontrol circuit means positioned within said housing, said circuit meansincluding a solid state controllable current conducting semiconductor,said semiconductor being mounted directly on said metal member withinsaid depression in conductive heat transfer relationship therewith.

2. A variable light intensity socket in accordance with claim 1 whereinsaid metal member further comprises a flange depending from at least theend portions of the curve periphery of said planar member and contactingthe adjacent surface of said support member, at least one invertedU-shaped ridge formed in said planar member and extending substantiallyperpendicularly to said support member and in contact therewith, said atleast one ridge being on the surface of said planar member opposite tothat of said flange to provide support for said planar member againstbending relative to said support member.

3. A variable light intensity socket in accordance with claim 2 furthercomprising an electrically conductive L-shaped angle bar, means forfastening one side of said angle bar to the end of said support memberwhich is adjacent to said base member, means for fastening the otherside of said angle bar through said base member to said shell, theexposed surface area of said angle bar being small compared to the areaof said base member.

4. A variable light intensity socket in accordance with claim 3 whereinsaid semiconductor is a controllable bidirectional current conductingsemiconductor.

5. A variable light intensity socket in accordance with claim 1 whereinsaid circuit means comprises a printed circuit formed on one side ofsaid support member, and circuit elements mounted on said supportmember.

6. A variable light intensity socket in accordance with claim 5 whereinsaid circuit. means further comprises a radio frequency filter networkincluding an inductance, said inductance being mounted on said supportmember adjacent said base member and remote from said heat sink member.

7. A variable light intensity socket in accordance with claim 1 furthercomprising an electrically conductive L-shaped lOlOIlS 017i

2. A variable light intensity socket in accordance with claim 1 whereinsaid metal member further comprises a flange depending from at least theend portions of the curve periphery of said planar member and contactingthe adjacent surface of said support member, at least one invertedU-shaped ridge formed in said planar member and extending substantiallyperpendicularly to said support member and in contact therewith, said atleast one ridge being on the surface of said planar member opposite tothat of said flange to provide support for said planar member againstbending relative to said support member.
 3. A variable light intensitysocket in accordance with claim 2 further comprising an electricallyconductive L-shaped angle bar, means for fastening one side of saidangle bar to the end of said support member which is adjacent to saidbase member, means for fastening the other side of said angle barthrough said base member to said shell, the exposed surface area of saidangle bar being small compared to the area of said base member.
 4. Avariable light intensity socket in accordance with claim 3 wherein saidsemiconductor is a controllable bidirectional current conductingsemiconductor.
 5. A variable light intensity socket in accordance withclaim 1 wherein said circuit means comprises a printed circuit formed onone side of said support member, and circuit elements mounted on saidsupport member.
 6. A variable light intensity socket in accordance withclaim 5 wherein said circuit means further comprises a radio frequencyfilter network including an inductance, said inductance being mounted onsaid support member adjacent said base member and remote from said heatsink member.
 7. A variable light intensity socket in accordance withclaim 1 further comprising an electrically conductive L-shaped anglebar, means for fastening one side of said angle bar to the end of saidsupport member which is adjacent to said base member, means forfastening the other side of said angle bar through said base member tosaid shell, the exposed surface area of said angle bar being smallcompared to the area of said base member.
 8. A variable light intensitysocket in accordance with claim 1 wherein said semiconductor is acontrollable bidirectional current conducting semiconductor.